1. Field of the Invention
The invention generally relates to vision diagnostics and, more particularly, to a method for providing improved objective manifest refraction values, an associated method for prescribing a vision correction, and apparatus associated therewith.
2. Description of Related Art
A phoropter is a fundamental optometric diagnostic instrument for vision measurement and evaluation for obtaining a manifest refraction; i.e., defocus and astigmatism (often referred to as “lower-order” aberrations) in an undilated eye. It essentially is a device with a large set of lenses on dials. The device is positioned for a patient to look through and give visual acuity feedback to the practitioner when a particular dialed lens is presented in front of the patient's eye. This method of manifest refractometry provides defocus and astigmatism information to the practitioner typically in order to prescribe vision correcting lenses for the patient. The subjective nature of the phoropter measurement process, from the patient's perspective, is itself a disadvantage of this form of refractometry. Practitioner error can also be problematic, especially when adequate practitioner training may be lacking as it often is in many underdeveloped areas of the world.
An autorefractor is a device that provides an objective diagnostic measurement of a patient's refraction. Although patient subjectivity has been removed from the measurement process, there are other disadvantages associated with autorefractors. First, they are expensive instruments. Second, autorefractor measurements are typically inaccurate, compared to a patient's subjective refraction. There are reports of measurement errors in up to 20% of the population measured in this way. In fact, up to a 2 Diopter (D) difference between the objective manifest refraction and subjective manifest refraction has been observed on an individual basis.
A wavefront sensor is a device that measures optical errors in terms of wavefront aberrations. The measured aberrations typically include monochromatic wavefront defects such as spherical aberration, coma, trilateral astigmatism and others, usually referred to as higher-order aberrations. Although wavefront sensing has been used for some time in astronomical and defense applications, the modification, use, and development of this technology in ophthalmology is relatively recent. Moreover, wavefront sensor data is not naturally indicative of manifest refraction. Yet, as vision correction technology advances, wavefront sensing instrumentation will, by necessity, consume office space and resources. Broadening the usefulness of such a tool will justify the costs associated with these instruments.
Based on the foregoing, the inventors have recognized the desirability of being able to accurately predict a manifest refraction based upon objective manifest refraction data, and do it efficiently. Thus, obtaining better measurements with less equipment and less expensive equipment is highly advantageous. The invention also provides an improvement in the ability to specify and prescribe vision correction, including lenses and refractive surgical treatment. Apparatus associated with the invention is further provided. These and other advantages and objects of the invention are described in detail below and with reference to the appended claims.